1. Field of the Invention
The present invention relates to electric arc apparatus and an associated method and, more specifically, it relates to means for effectively resisting formation of undesired surface irregularities in the ingot created in such apparatus.
2. Description of the Prior Art
It has been known previously to employ vacuum electric arc furnaces wherein a consumable electrode is Cprogressively melted by means of an electric current which is run through the electrode and arcs to molten metal contained within a crucible. The consumable electrode is progressively advanced into the crucible so as to maintain the desired spacing between the electrode and the molten metal bath. It is known to employ a copper-walled crucible inside of a jacket through which cooling material such as water, for example, is passed.
With respect to such systems, surface irregularities on the resultant ingot have generally made it necessary to grind the surface in order to obtain the desired smooth surface. Surface irregularities may be caused by spatter. Spatter may be produced by the force of the electric arc causing globules of metal to be thrown into contact with the cold crucible wall above the molten pool level where chilling causes the globules to freeze into a porous nonhomogeneous mass. Also, gases evolving from the molten pool, as well as from the molten metal being discharged from the electrode, may serve to cause metal droplets to be deposited and solidified on the interior wall of the crucible. As the level of the molten pool rises, some of the liquid metal from the pool partially fuses to the porous mass along the crucible wall to produce an undesired matted surface on the ingot. Not only do such irregularities require additional processing steps to establish a uniform smooth exterior surface on the ingot, but some loss of metal is also involved.
U.S. Pat. No. 3,636,228 discloses the use of a transducer in a servo system which provides information regarding the position of an arc.
U.S. Pat. No. 3,680,163 discloses a system wherein the purification of metals, a field coil disposed within an electrode assists with effecting stirring of the melt through its influence on the arc.
U.S. Pat. No. 2,849,658 discloses pole pieces of limited scope which are adapted to provide a narrow magnetic field within the furnace. U.S. Pat. No. 2,652,440 also discloses a system wherein several local pole pieces generate narrow magnetic fields.
U.S. Pat. No. 3,683,094 discloses an arc furnace which has a rotating electrode wheel. The field imposed by the three coils tends to restrain the rotational movement of the arc produced by the rotating electrode wheel.
In spite of these prior art disclosures there remains a very real and substantial need for an effective vacuum arc furnace which will produce an ingot which possesses the desired surface smoothness.